REPLICATION OF BACILLUS-THURINGIENSIS IN LARVAE OF THE MEDITERRANEAN FLOUR MOTH, EPHESTIA-KUEHNIELLA (LEPIDOPTERA, PYRALIDAE) - GROWTH, SPORULATION AND INSECTICIDAL ACTIVITY OF PARASPORAL CRYSTALS

Spores and parasporal crystals of a Bacillus thuringiensis serovar aiz awai strain were fed to fifth instar larvae of the Mediterranean flour moth, Ephestia kuehniella, under laboratory conditions. Viable number s of B. thuringiensis cells in E. kuehniella larvae were estimated by dilution-plating on peptone-polymyxin agar medium, and combined spore and crystal insecticidal activity was bioassayed with larvae of Bombyx mori. B. thuringiensis rapidly grew and sporulated in the larval cada vers of E. kuehniella regardless of inoculation dose. Spores that were produced in situ in E. kuehniella cadavers persisted for at least 90 d. Insecticidal activity of the homogenates of E. kuehniella cadavers fluctuated along with the viable cell numbers and persisted for at lea st 90 d. To examine horizontal transmission of B. thuringiensis in E. kuehniella larval populations, B. thuringiensis-infected and healthy l arvae were released into containers in various proportions, but no rel iable transmission was detected under our experimental conditions.